Q. 6 4.3( 57 Votes )

H2S, a toxic gas with rotten egg like smell, is used for the qualitative analysis. If the solubility of H2S in water at STP is 0.195 m, calculate Henry’s law constant.

Answer :

According to Henry's law,

"At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid."

Stated as,

p = KHx


P = partial pressure of the solute above the solution

KH = Henry's constant

x = concentration of the solute in the solution


Solubility of H2S in water at STP is 0.195 m

We know,

At STP pressure p = 0.987 bar.

0.195 mol of H2S is dissolved in 1000g of water

Moles of water =

= 55.56 g/mol

the mole fraction of H2S =


= 0.0035

According to Henry's law,

p = KHx

KH =

KH =

KH = 282 bar

The Henry’s law constant is 282 bar

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